[ARM/AArch64] Support FP16 +fp16fml instructions

Add +fp16fml feature for new FP16 instructions, which are a
mandatory part of FP16 from v8.4-A and an optional part of FP16
from v8.2-A. It doesn't seem to be possible to model this in
LLVM, but the relationship between the options is handled by
the related clang patch.

In keeping with what I think is the usual practice, the fp16fml
extension is accepted regardless of base architecture version.

Builds on/replaces Sjoerd Meijer's patch to add these instructions at
https://reviews.llvm.org/D49839.

Differential Revision: https://reviews.llvm.org/D50228

llvm-svn: 340013
diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.h b/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
index e0cd2d8..7d14bd7 100644
--- a/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
+++ b/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
@@ -57,7 +57,7 @@
   const FeatureBitset InlineFeatureWhitelist = {
       ARM::FeatureVFP2, ARM::FeatureVFP3, ARM::FeatureNEON, ARM::FeatureThumb2,
       ARM::FeatureFP16, ARM::FeatureVFP4, ARM::FeatureFPARMv8,
-      ARM::FeatureFullFP16, ARM::FeatureHWDivThumb,
+      ARM::FeatureFullFP16, ARM::FeatureFP16FML, ARM::FeatureHWDivThumb,
       ARM::FeatureHWDivARM, ARM::FeatureDB, ARM::FeatureV7Clrex,
       ARM::FeatureAcquireRelease, ARM::FeatureSlowFPBrcc,
       ARM::FeaturePerfMon, ARM::FeatureTrustZone, ARM::Feature8MSecExt,